Basically, I need a way to return control to the beginning of a for loop and actually restart the entire iteration process after taking an action if a certain condition is met.
What I'm trying to do is this:
for index, item in enumerate[list2]:
if item == '||' and list2[index-1] == '||':
del list2[index]
**
That way, if ['berry','||','||','||','pancake] is inside the list, I'll wind up with:
['berry','||','pancake'] instead.
Thanks!
asked Sep 13, 2010 at 22:34
GeorginaGeorgina
3811 gold badge6 silver badges13 bronze badges
6
I'm not sure what you mean by "restarting". Do you want to start iterating over from the beginning, or simply skip the current iteration?
If it's the latter, then for loops support continue just like while loops do:
for i in xrange[10]:
if i == 5:
continue
print i
The above will print the numbers from 0 to 9, except for 5.
If you're talking about starting over from the
beginning of the for loop, there's no way to do that except "manually", for example by wrapping it in a while loop:
should_restart = True
while should_restart:
should_restart = False
for i in xrange[10]:
print i
if i == 5:
should_restart = True
break
The above will print the numbers from 0 to 5, then start over from 0 again, and so on indefinitely [not really a great example, I know].
answered Sep 13, 2010 at 22:44
Liquid_FireLiquid_Fire
6,8802 gold badges24 silver badges22 bronze badges
3
while True:
for i in xrange[10]:
if condition[i]:
break
else:
break
That will do what you seem to want. Why you would want to do it is a different matter. Maybe you should take a look at your code and make sure you're not missing an obvious and easier way to do it.
answered Sep 13, 2010 at 22:44
nmichaelsnmichaels
48.1k12 gold badges102 silver badges132 bronze badges
1
some action that resarts the whole process
A poor way to think of an algorithm.
You're just filtering, i.e., removing duplicates.
And -- in Python -- you're happiest making copies, not trying to do del. In general, there's very little call to use del.
def unique[ some_list ]:
list_iter= iter[some_list]
prev= list_iter.next[]
for item in list_iter:
if item != prev:
yield prev
prev= item
yield prev
list[ unique[ ['berry','||','||','||','pancake'] ] ]
answered Sep 13, 2010 at 22:56
S.LottS.Lott
376k78 gold badges503 silver badges771 bronze badges
5
The inevitable itertools version, because it just came to me:
from itertools import groupby
def uniq[seq]:
for key, items in groupby[seq]:
yield key
print list[uniq[['berry','||','||','||','pancake']]] # ['berry','||', 'pancake']
# or simply:
print [key for key, items in groupby[['berry','||','||','||','pancake']]]
answered Sep 13, 2010 at 23:26
Jochen RitzelJochen Ritzel
102k29 gold badges195 silver badges190 bronze badges
1
Continue will work for any loop.
answered Sep 13, 2010 at 22:37
voltingvolting
15k7 gold badges34 silver badges54 bronze badges
2
continue works in for loops also.
>>> for i in range[3]:
... print 'Before', i
... if i == 1:
... continue
... print 'After', i
...
Before 0
After 0
Before 1
# After 1 is missing
Before 2
After 2
answered Sep 13, 2010 at 22:39
Sam DolanSam Dolan
31.3k9 gold badges84 silver badges84 bronze badges
1
As you can see answering your question leads to some rather convoluted code. Usually a better way can be found, which is why such constructs aren't built into the language
If you are not comfortable using itertools, consider using this loop instead. Not only is it easier to follow than your restarting for loop, it is also more efficient because it doesn't waste time rechecking items that have already been passed over.
L = ['berry','||','||','||','pancake']
idx=1
while idx